Polymorphise meta tree labels

src/TreeHelp.hs

@@ -24,9 +24,11 @@ module TreeHelp
     , updateRandNode
     , safeUpdateSingleNode
     , msafeUpdateSingleNode
+    , numTraversable
     ) where
 import RandomHelp
 
+import Data.Traversable
 import Data.Maybe
 import Data.Tree.Lens
 import Data.Tree
@@ -183,15 +185,11 @@ splitTrunk t = do
     i <- state $ randomR (0, trunkDepth t)
     return $ splitTrunkAt i t
 
+numTraversable :: Traversable t => t a -> t (a,Int)
+numTraversable = snd . mapAccumL f 0
+  where
+    f i x = (i+1,(x,i))
+
 -- untested
 inorderNumberTree :: Tree a -> Tree (a,Int)
-inorderNumberTree = fst . f 0
-  where
-    f i (Node x ts) =
-        let (ts',i') = g (i+1) ts
-        in (Node (x,i) ts', i')
-    g i (t:ts) = 
-        let (t',i') = f i t
-            (ts',i'') = g i' ts
-        in (t': ts', i'')
-    g i [] = ([], i)
+inorderNumberTree = numTraversable